If it's stingers that are the threat (could be some other type), you're OK over FL150. The range and the ceiling are distinct.
So does the stinger know that it's being fired from the top of a 15000 ft mountain? and think, nope, I am not gonna go above FL150, I am just not doing it I tell you! It is perhaps a relief that nobody here will be taking your cast iron reassurances. Try 15000ft agl.